The present invention generally relates to a method to control motion in a machine having a number of inter-related movement devices and, more specifically, to the synchronization of the motion between the gathering transport and the enclosure feeders in a mail inserter system.
In a mail inserting machine for mass mailing, there is a gathering section where enclosure material is gathered before it is inserted into an envelope. This gathering section is sometimes referred to as a chassis subsystem, which includes a gathering transport with pusher fingers rigidly attached to a conveying belt and a plurality of enclosure feeders mounted above the gathering transport. If the enclosure material contains many documents, these documents must be individually and separately fed from different enclosure feeders. Each of the enclosure feeders feeds or releases a document at an appropriate time such that the trailing edge of the document released from the enclosure feeder is just slightly forward of a moving pusher finger. Timing and velocity control of all feeders are critical because during the feeding process a document is under the control of both an enclosure feeder motor and the gathering transport motor.
Currently, one or more long endless chains driven by a single motor are used to move the pusher fingers in order to gather the enclosure material released from the enclosure feeders and then send the gathered material to an insertion station. It is preferable that the spacing of the pusher fingers attached to the conveying chain is substantially the same as the spacing of the enclosure feeders mounted above the conveying chain. A typical pitch of the enclosure feeder is 13.5xe2x80x3 (343 mm). Depending on the length of the document stacked on a feeder, the feeder is given a Agoxe2x89xa1signal to release a sheet of a document onto the conveying belt at an appropriate time. Typically, the feeder motor is set in motion only for releasing a document to an approaching pusher finger. After the document is released, the feeder motor is stopped to wait for the arrival of the next pusher finger. The conveyor belt, however, must be continuously driven in order to gather documents released by different enclosure feeders. Thus, the motion profile of the chassis is different from that of the enclosure feeders. Moreover, when the enclosure material contains documents of different lengths, the start and stop timing for one feeder motor may be different from another. The existence of different motion profiles of the feeder motors will make synchronization between the chassis motor and all feeder motors difficult. However, probably the most difficult motion to synchronize is when a chassis is required to stop and restart at any time in a machine cycle.
In the past, electronic gearing has been used to synchronize the motion between a number of motors. Electronic gearing uses electronic means to maintain the motion profiles between two or more motors, instead of using mechanical gears, or belts and pulleys. For example, pulse generators of different pulse rates can be used to drive different motors. If the pulse rates are maintained at a fixed ratio, then the motion profiles of motors would be similar. This is equivalent to using mechanical gears at a fixed gear ratio to drive different shafts by the same motor. In order to maintain the synchronism between motors in electronic gearing, encoders attached to motors can be used to monitor the ratio of the displacement between motors. If the speed ratio of two motors is a constant, then it is expected that the ratio of the encoder readings from the respective motors is also a constant. However, if the speed ratio between two motors is not constant, the above-described method of electronic gearing will become impractical, if not totally infeasible.
It is advantageous to provide a method for monitoring and controlling motion between different moving devices wherein the speed ratio can be varied with time.
The present invention provides a displacement mapping method and apparatus to synchronize the motion between a master motor and one or more slave motors wherein the motion profile of one motor can be varied with time independently of the others. The displacement mapping method uses encoders, such as optical encoders, to obtain the displacement of each of the associated motors as a function of time. From the actual displacement of the master motor, an electronic computation device or process is used to calculate the theoretical displacement of each slave motor according the motion profile of the slave motor. The theoretical displacement is then compared to the actual displacement. If there is a discrepancy between the theoretical and the actual amount then the motion of the slave motor will be adjusted so as to eliminate that displacement discrepancy.
In general, the method includes the steps of obtaining the displacement transformation function at each commanded position and mapping the actual displacement of the master motor onto the displacement of the slave motor using the transformation function. The result of the displacement mapping is the theoretical displacement of the slave motor. The theoretical displacement is then compared to the actual displacement of the slave motor. The synchronism between the master and slave motors can be achieved by adjusting the speed of the slave motor based on the comparison.
It should be noted that, the relationship between the motion profile of each slave motor and the motion profile of the master motor, in general, is not linear. For example, the slave motors in an inserting machine may start and stop within a feeding cycle while the master motor has a constant speed. Accordingly, the transformation function is nonlinear. Moreover, the speed of the master motor can be changed while the synchronism between the master motor and slave motors is maintained.
The present invention will become apparent upon reading the description taken in conjunction with FIG. 1 to FIG. 5B.